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    <title>Document</title>
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    <script>
        //var 声明的变量往往会越域
        //let 声明的变量有严格局部作用域
        // {
        //     var a = 1;
        //     let b = 2;
        // }
        // console.log(a);
        // console.log(b);
        // var m = 1;
        // var m = 2;
        // let n = 1;
        // let n = 2;


        // console.log(x);
        // var x = 10;
        // console.log(y);
        // let y = 20;

            const a = 1;
            a = 3;


    </script>
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